As somebody already said, definitely play on normal difficulty, to clear the shards as fast as possible. It seems like the chance for the light blue shrine to spawn below SR 50 is really, really low (if it is even possible at all). I played from SR 25 to SR 50 in one session and have not seen it once, google seems to confirm that is also the experience others had.
I have seen the light blue shrine between SR 50 and SR 75 in 2 out of 3 runs, so starting at SR 50 is my personal recommendation.
In terms of items, yeah I would definitely duplicate items on Xbox, or use GD Stash/GD Defiler on PC, but that’s also a personal choice.
For the summon 18 pets achievement, don’t worry too much about that. It’s not that hard to get, if you have the right items and devotions.